ART: Add allocation callback

Bug: 31684277
Test: m test-art-host
Change-Id: I959f44e23ca5fe55ed678315708895faf0aadb04
diff --git a/runtime/openjdkjvmti/events-inl.h b/runtime/openjdkjvmti/events-inl.h
index b298301..d027201 100644
--- a/runtime/openjdkjvmti/events-inl.h
+++ b/runtime/openjdkjvmti/events-inl.h
@@ -29,6 +29,9 @@
     return nullptr;
   }
 
+  // TODO: Add a type check. Can be done, for example, by an explicitly instantiated template
+  //       function.
+
   switch (event) {
     case JVMTI_EVENT_VM_INIT:
       return reinterpret_cast<FnType*>(env->event_callbacks->VMInit);